1. Technical Field
The present disclosure relates to a thread cutter for a sewing machine, which is provided on an underside of a needle plate having a needle hole and cuts needle and bobbin threads located between a workpiece cloth and a rotary hook including an outer rotating hook and an inner bobbin case.
2. Description of the Related Art
Conventional sewing machines have been provided with thread cutters. The thread cutter is provided on an underside of a needle plate having a needle hole and cuts needle and bobbin threads located between a workpiece cloth and a rotary hook including an outer rotating hook and an inner bobbin case. For example, Japanese patent application publication JP-A-H03-210298 (hereinafter referred to as “related art document 1”) discloses a thread cutter of the above-described type, in which a thread cutting cam mounted on a lower shaft of a sewing machine is actuated by a sewing machine motor so that a moving blade is driven. The moving blade and a fixed blade are caused to cooperate with each other thereby to cut needle and bobbin threads. The thread cutter disclosed by related art document 1 is provided with the moving and fixed blades as a cutting blade, and the moving blade is driven by the sewing machine motor to be caused to cooperate with the fixed blade. As a result, the thread cutter has a complicated construction.
In order to overcome the complicated construction, Japanese patent application publication JP-2003-284878 (hereinafter referred to as “related art document 2”) discloses another thread cutter for a sewing machine. The thread cutter disclosed by related art document 2 includes a stepping motor serving as a dedicated drive source for driving a thread seizing assembly. The thread cutter further includes a fixed blade as a cutting blade. The thread seizing assembly has a distal end which is reciprocally moved above a bobbin case thereby to seize the needle and bobbin threads. The seized needle and bobbin threads are cut by the fixed blade mounted on a proximal end side of the thread seizing assembly.
The thread cutter disclosed by related art document 2 has a simple construction since the thread seizing assembly is driven by the stepping motor. However, the needle and bobbin threads are cut by the fixed blade mounted on the proximal end side of the thread seizing assembly. Accordingly, the location of the fixed blade is spaced farther away from the needle hole of the needle plate than in the thread cutter of related art document 1. As a result, an amount of needle and bobbin threads remaining at the workpiece cloth side after thread cutting (remaining amounts of threads at the workpiece cloth side) is increased disadvantageously. Furthermore, the thread cutter of related art document 2 has another disadvantage that an amount of needle thread remaining in a section from an eye of a needle attached to a needlebar to a thread end (a remaining amount of thread at the needle side) also becomes larger than a proper amount necessitated for stitch forming in a subsequent sewing operation. When an extra amount of threads remains at the workpiece cloth and needle sides, there is a possibility of occurrence of failure or trouble such as thread entanglement in an initial stitch upon start of a subsequent sewing operation. Additionally, the extra thread ends need to be manually cut after completion of the sewing operation.